GHC Exactprint merge process

Richard Eisenberg rae at
Thu Mar 11 23:48:34 UTC 2021

I've started a review, but sent along what I had when dinner was ready. Hopefully more later, but don't wait up for me!

Incidentally: this is a monstrous patch, and so there is a strong incentive just to get on with it without resolving all these quibbles. I won't stand in your way on that front -- it might be better to improve this after it lands. However, I also see quite a few TODO:AZ notes. Are you intending to fix these before landing? Or do you think it's OK to merge first and then return?

High level piece: I'm in support of this direction of movement -- I just want to make sure that the new code is understandable and maintainable.


> On Mar 6, 2021, at 12:39 PM, Alan & Kim Zimmerman <alan.zimm at> wrote:
> I have been running a branch in !2418[1] for just over a year to migrate the ghc-exactprint functionality directly into the GHC AST[2], and I am now satisfied that it is able to provide all the same functionality as the original.
> This is one of the features intended for the impending 9.2.1 release, and it needs to be reviewed to be able to land.  But the change is huge, as it mechanically affects most files that interact with the GHC AST.
> So I have split out a precursor !5158 [3] with just the new types that are used to represent the annotations, so it can be a focal point for discussion.
> It is ready for review, please comment if you have time and interest.
> Regards
>   Alan
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> [2] <>
> [3] <>_______________________________________________
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